Ion beam target assemblies for neutron generation

ABSTRACT

Provided herein are systems, devices, articles of manufacture, and methods for generating neutrons employing a high energy ion beam target (HEM target) and a target backing configured to be in contact with the bottom surface of the HEIB target (e.g., to generate an ion beam target assembly). In certain embodiments, the HEM target has a thickness that is less than the penetration depth of protons or deuterons in the high energy ion beam that strikes the target. In certain embodiments, the target backing comprises a high hydrogen diffusion metal (e.g., palladium), has open spaces dispersed throughout for reduced proton diffusion distances, and has a shape and thickness such that all, or virtually all, of the protons or deuterons that pass through the HEIB target are stopped. Also provided herein are systems, devices, and methods for changing targets in an ion beam accelerator system.

The present application is a continuation of U.S. application Ser. No.16/430,839, filed Jun. 4, 2019, which claims priority to U.S.Provisional application Ser. No. 62/681,432, filed Jun. 6, 2018, whichis herein incorporated by reference in its entirety.

FIELD

Provided herein are systems, devices, articles of manufacture, andmethods for generating neutrons employing a high energy ion beam target(HEM target) and a target backing configured to be in contact with thebottom surface of the HEIB target (e.g., to generate an ion beam targetassembly). In certain embodiments, the HEM target has a thickness thatis less than the penetration depth of protons in the high energy ionbeam that strikes the target. In certain embodiments, the target backingcomprises a high hydrogen diffusion metal (e.g., palladium), has openspaces dispersed throughout for reduced proton or deuteron diffusiondistances, and has a shape and thickness such that all, or virtuallyall, of the protons or deuterons that pass through the HEIB target arestopped. Also provided herein are systems, devices, and methods forchanging targets in an ion beam accelerator system.

BACKGROUND

A known method to produce neutrons is to bombard a Beryllium (Be) targetwith high energy (>2 MeV) protons. The Beryllium needs to be cooled toprevent melting and/or thermal distortion. Typical geometry is a Be diskbrazed to a water-cooled block, or a Be block sealed to a holder anddirectly cooled on the back side (away from beam) by water or otherfluid. A consistent problem with this method is that embedded protonsembrittle and swell the material in which they are embedded. Eventually,this results in direct physical degradation (spalling) of the target.The typical embedded dose limit before visible target damage is about10¹⁸ protons/cm². In high power density systems, visible damage canoccur in minutes of exposure.

One approach to mitigate this issue is by making the Be target thinnerthan the stopping distance of the protons so that relatively few protonsare deposited into the Be. The depth that the protons penetrate amaterial depends on the proton energy and material in which the protonsare deposited into. In the case of the Be target that is directlyfluid-cooled, the protons are deposited into the cooling fluid and noswelling occurs. However, the Be target is the vacuum barrier andsubject to damage from the proton beam. Target lifetime would bestochastic, and a failure would result in catastrophic flooding of thevacuum system requiring a conservative replacement schedule. In the caseof the Be target mounted to a fluid-cooled substrate, the protons aredeposited in the substrate that is subject to the same blistering andspalling damage. However, by choosing substrate materials that canabsorb a relatively large amount of hydrogen, the lifetime of the targetcan be increased. For example, tantalum can hold about 100 to 1000 timesthe amount of hydrogen than Be before damage. In high power systems,this can result in target lifetimes measured in 100's of hours or more,but still finite. In such cases, the creation of high neutron fluxeswill cause materials to become activated. What is needed are designsthat can be optimized to reduce the production of long-lived radioactiveisotopes. This will allow for easier and safer handling and maintenanceof the targets and higher uptime for the device in which they areutilized.

SUMMARY

Provided herein are systems, devices, articles of manufacture, andmethods for generating neutrons employing a high energy ion beam target(HEM target) and a target backing configured to be in contact with thebottom surface of the HEIB target (e.g., to generate an ion beam targetassembly). In certain embodiments, the HEM target has a thickness thatis less than the penetration depth of protons in the high energy ionbeam that strikes the target. In some embodiments, the HEM targetcomprises a metal selected from beryllium, uranium, lithium, a lithiumcompound, tungsten, and tantalum. In certain embodiments, the highenergy ion beam comprises protons and/or deuterons. In certainembodiments, the target backing comprises a high hydrogen diffusionmetal (e.g., palladium), has open spaces dispersed throughout forreduced proton or deuteron diffusion distances, and has a shape andthickness such that all, or virtually all, of the protons or deuteronsthat pass through the HEIB target are stopped. In some embodiments, thehigh energy ion beam comprises hydrogen ions or deuterium ions. Alsoprovided herein are systems, devices, and methods for changing targetsin an ion beam accelerator system.

In some embodiments, provided herein are systems comprising: a) a highenergy ion beam target (HEIB target) having a top surface and a bottomsurface, wherein the HEIB target generates neutrons when exposed to ahigh energy ion beam, and wherein the HEIB target has a thicknessbetween the top and bottom surfaces that is less than the penetrationdepth of protons in the high energy ion beam; and b) a target backingcomprising a high hydrogen diffusion metal (HHDM), wherein the targetbacking has open spaces dispersed throughout such that the proton ordeuteron diffusion distance is reduced throughout the target backingcompared to if the target backing was a solid piece without the openspaces, wherein the target backing is configured to be positioned incontact with the bottom surface of the HEIB target, and wherein thetarget backing has a shape and thickness such that all, or virtuallyall, of the protons or deuterons in the higher energy ion beam that passthrough the HEM target are stopped by the target backing when it ispositioned in contact with the HEIB target. In certain embodiments, theion beam comprises protons. In other embodiments, the ion beam comprisesdeuterons. In some embodiments, the HEM target comprises a metalselected from beryllium, uranium, lithium, a lithium compound, tungsten,and tantalum.

In certain embodiments, provided herein are articles of manufacturecomprising: a) an ion beam target assembly, wherein the ion target beamassembly comprises: i) a high energy ion beam target (HEIB target)having a top surface and a bottom surface, wherein the HEIB targetgenerates neutrons when exposed to a high energy ion beam, and whereinthe HEIB target has a thickness between the top and bottom surfaces thatis less than the penetration depth of protons in the high energy ionbeam; and ii) a target backing comprising a high hydrogen diffusionmetal (HHDM), wherein the target backing has open spaces dispersedthroughout such that the proton or deuteron diffusion distance isreduced throughout the target backing compared to if the target backingwas a solid piece without the open spaces, wherein the target backing isattached to the bottom surface of the HEIB target, and wherein thetarget backing has a shape and thickness such that all, or virtuallyall, of the protons or deuterons in the higher energy ion beam that passthrough the HEIB target are stopped by the target backing. In someembodiments, the HEIB target comprises a metal selected from beryllium,uranium, lithium, a lithium compound, tungsten, and tantalum.

In particular embodiments, provided herein are methods of generatingneutrons comprising: a) inserting both the HEM target and the targetbacking (in contact with each other), or an ion beam target assembly, asdescribed herein, into a target chamber of an ion beam acceleratorsystem, and b) generating a high energy ion beam with the ionaccelerator system such that the high energy ion beam strikes the HEMtarget, thereby generating neutrons. In certain embodiments, the methodsfurther comprise: c) collecting at least some of the neutrons. In otherembodiments, step b) is conducted continuously for at least 2 days(e.g., 2 . . . 5 . . . 20 . . . 45 . . . 100 . . . 1000 days) withoutfailure of the HEIB target. In further embodiments, step b) is conductedcontinuously for at least 14 days without failure of the HEIB target.

In some embodiments, the open spaces in the target backing are selectedfrom: pores, grooves, holes, corrugations, channels, open cells,honeycomb cells, dimples, irregular openings, or any combinationthereof. In certain embodiments, the target backing is attached to, orconfigured to be attached to, the bottom surface of the HEIB target bybrazing, welding, diffusional bonding, or any other method that resultsin a low thermal resistance.

In particular embodiments, the systems and articles of manufacturefurther comprise a cooled substrate. In some embodiments, the targetbacking is attached to, or configured to be attached to, the cooledsubstrate. In further embodiments, the cooled substrate comprises awater cooled substrate or glycol cool substrate. In other embodiments,the cooled substrate comprises copper and/or aluminum.

In some embodiments, the HEIB target comprises: i) a first layercomprising a metal (e.g., beryllium, uranium, lithium, tungsten, andtantalum), and ii) a second layer comprising a metal different than usedin said first layer selected from the group consisting of: beryllium,uranium, lithium, tungsten, and tantalum. In certain embodiments, theHEIB target comprises a first layer comprised of beryllium and a secondlayer comprises of uranium. In certain embodiments, using multiplelayers in the target are employed to slow down the ion beam as ittraverses the target, slowing it down from its original energy to lowerenergies (mostly due to electron interactions). In some embodiments,using different materials at different lengths (energies) along the beampath allows a better optimization of neutron yield, energy, and angulardistribution.

In some embodiments, HEIB target has a thickness between 1 and 15 mm(e.g., 1 . . . 3 . . . 10 . . . 12 . . . and 15 mm), and a diameterbetween 20 and 100 mm (e.g., 20 . . . 45 . . . 65 . . . and 100 mm). Incertain embodiments, the thickness of the target backing is between 2and 10 mm (e.g., 2 . . . 5 . . . 7.5 . . . and 10 mm). In someembodiments, the HEIB target and the target backing are generally diskshaped, square shaped, octagon shaped, ellipsoidal, rectangular, andhave the same diameter. The HEM target may also be designed to such thatthe high energy ion beam strikes the target at an incident angle of 90°,or an incident angle other than 90° (e.g. 45° . . . 60° . . . 30°,etc.), which has the effect of increasing the area over which the beamstrikes the target, thus reducing the power density of the beam by thegeometric amount. In some embodiments, such targets have an ellipsoidal,rectangular, or other elongated shape in the direction of the targettilt.

In certain embodiments, at least 94% of the HEIB target is a metalselected from beryllium, uranium, lithium, a lithium compound, tungsten,and tantalum (e.g., 95% . . . 98% . . . 99% . . . or 100%). In furtherembodiments, the high hydrogen diffusion metal (HHDM) comprisespalladium. In other embodiments, the high hydrogen diffusion metal(HHDM) is selected from the group consisting of: palladium, titanium,vanadium, niobium, zirconium, and any combination thereof (e.g.,combination of vanadium and palladium). In particular embodiments, theHHDM is composed of a combination of these elements, specifically with aless expensive material (e.g. vanadium) coated with a thin layer of amore expensive material (e.g. palladium) known to have superior hydrogensurface diffusion properties. In some embodiments, at least 94% of thetarget backing is the high hydrogen diffusion metal (HHDM) (e.g., 95% .. . 97.5% . . . 99% . . . or 100%). In certain embodiments, the targetbacking is composed of a solid vanadium core that is coated with a thinfilm of palladium.

In additional embodiments, the systems and articles of manufacturefurther comprise: a target chamber. In certain embodiments, the targetbacking is positioned at (e.g., attached to) the bottom surface of theHEM target thereby generating an ion beam target assembly, wherein theion beam target assembly is located in the target chamber. In otherembodiments, the systems and articles of manufacture further comprise:an ion source configured to produce a ion beam (e.g., proton beam ordeuteron beam); and an accelerator operatively coupled to the ion sourceand configured to receive the ion beam and accelerate the ion beam togenerate the high energy ion beam. In further embodiments, the targetbacking is attached to the bottom surface of the HEM target therebygenerating an ion beam target assembly, and wherein the system furthercomprises: a target chamber containing the ion beam target assembly. Infurther embodiments, the ion beam target assembly is sized andpositioned inside the target chamber such that failure of the HEIBtarget does not result in vacuum breach in the accelerator.

In some embodiments, the protons or deuterons in the high energy ionbeam are >2 MeV protons or deuterons. In further embodiments, the HEIBtarget can be struck with the high energy ion beam for at least 24 hourstotal time longer (e.g., 24 . . . 50 . . . 100 . . . or 1000 hourslonger) before failure when the backing component is positioned incontact with the bottom surface of the HEIB target, as compared to theHEIB target when not positioned in contact with the backing component.In further embodiments, the HEIB target can be struck with the highenergy ion beam for at least 7 days total time longer (e.g., 7 . . . 25. . . 100 . . . 1000 days longer) before failure when the backingcomponent is positioned in contact with the bottom surface of the HEIBtarget, as compared to the HEIB target when not positioned in contactwith the backing component.

In additional embodiments, provided herein are systems comprising: a) anion source configured to produce an ion beam; b) an acceleratoroperatively coupled to the ion source and configured to receive the ionbeam and accelerate the ion beam to generate an accelerated ion beam; c)a target chamber comprising a target holding mechanism, wherein thetarget holding mechanism is configured to: i) hold a target that, whenstruck with the accelerated ion beam, generates neutrons and becomes aradioactive target over time, and ii) allow the radioactive target to beremoved from the target chamber using at least one long-handled toolthat keeps a user of the long-handled tool from being irradiated.

In certain embodiments, provided herein are methods comprising: a)inserting a first target, from a set of at least two targets, into anion beam accelerator, b) activating the ion beam accelerator for alength of time such than an ion beam strikes the first target, therebygenerating neutrons and causing the first target to become a firstradioactive target; c) removing the first radioactive target from theion beam accelerator; d) inserting a second target, from the set of atleast two targets, into the ion beam accelerator; e) activating the ionbeam accelerator for a length of time such than ion beam strikes thesecond target, thereby generating neutrons and causing the second targetto become a second radioactive target; f) identifying that the firstradioactive target has cooled over time to become substantially or fullynon-radiative to generate a cooled first target, and inserting thecooled first target into the ion beam accelerator; and g) activating theion beam accelerator for a length of time such that an ion beam strikesthe cooled first target, thereby generating neutrons and causing thefirst cooled target to become re-radioactive first target.

In certain embodiment, the at least two targets is at least five targetswhich includes the first and second targets, as well as third, fourth,and fifth targets, and wherein steps a) and b) are repeated using thethird target, then the fourth target, and then the fifth target. Inother embodiments, steps f) and g) are repeated using the second, third,fourth, and fifth targets after they have cooled. In additionalembodiments, the at least two targets is at least ten targets.

In some embodiments, provided herein are systems comprising: a) an ionsource configured to produce an ion beam; b) an accelerator operativelycoupled to the ion source and configured to receive the ion beam andaccelerate the ion beam to generate an accelerated ion beam; c) a targetchamber configured to receive the accelerated ion beam; and d) a targetchanging mechanism, wherein the target changing mechanism is configuredto: i) hold a plurality of targets, wherein each target, when struckwith the accelerated ion beam in the target chamber generates neutrons,ii) hold one of the plurality of targets in a first position that isinside the target chamber and is in the path of the accelerated ionbeam, while holding the remaining targets outside the target chamber,and iii) move the target in the first position to a position outside thetarget chamber, and move one of the remaining targets into the firstposition inside the target chamber. In further embodiments, the at leastone of the plurality of targets, when not in the first position, are ina position outside the chamber that allows any accumulated radiation tosubstantially or fully dissipate. In other embodiments, the at least oneof the plurality of targets, when not in the first position, can beremoved from the system without stopping or disrupting the operation ofthe accelerated ion beam. In certain embodiments, the target changingmechanism comprises a carousel, turret, or magazine (e.g., that allowtargets to be moved without human intervention, or without humanintervention beyond activating the target changing mechanism). Inparticular embodiments, the at least one of the plurality of targets,when not in the first position, is automatically deposited into aradiation container. In additional embodiments, the target changingmechanism is further configured to allow one or more additional targetsto be added and held by the target changing mechanism without stoppingor disrupting the operation of the accelerated ion beam.

In certain embodiments, provided herein are devices comprising: a targetchanging mechanism for an ion beam accelerator having a target chamber,wherein the target changing mechanism is configured to: a) hold aplurality of targets, wherein each target, when struck with anaccelerated ion beam in the target chamber generates neutrons, b) holdone of the plurality of targets in a first position that is inside thetarget chamber and is in the path of the accelerated ion beam, whileholding the remaining targets outside the target chamber, and c) movethe target in the first position to a position outside the targetchamber, and move one of the remaining targets into the first positioninside the target chamber.

In certain embodiments, the target, target holding mechanism, targetchamber, braze and/or weld materials, fasteners, and all othercomponents are selected to minimize the production of long-lived (e.g.120 day half-life) radioactive isotopes resulting from neutron captureand other neutron reactions. Utilization of these materials will allowfor easier and safer handling and maintenance of the targets and higheruptime for the device in which they are utilized. Furthermore, reductionof the activity of the target allows for easier licensing and disposal.Exemplary materials include aluminum, vanadium, aluminum bronzes, andaluminum-based brazes (e.g. 1100 and 4043).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an exemplary schematic of a cross-section of an ion beamtarget assembly composed of a high energy ion beam target (e.g.,composed of beryllium) attached to a high hydrogen diffusion metaltarget backing (e.g., composed of palladium) with open spaces. The ionbeam target assembly is shown attached to a cooled substrate (e.g.,which is composed of copper or aluminum). FIG. 1B shows a close upsection of the exemplary ion beam target assembly from FIG. 1A, showingclose up detail of the open spaces in the target backing.

DETAILED DESCRIPTION

Provided herein are systems, devices, articles of manufacture, andmethods for generating neutrons employing a high energy ion beam target(HEM target) and a target backing configured to be in contact with thebottom surface of the HEIB target (e.g., to generate an ion beam targetassembly). In certain embodiments, the HEM target has a thickness thatis less than the penetration depth of protons in the high energy ionbeam that strikes the target. In some embodiments, the HEM targetcomprises a metal selected from beryllium, uranium, lithium, a lithiumcompound, tungsten, and tantalum. In certain embodiments, the ion beamcomprises protons. In other embodiments, the ion beam comprisesdeuterons. In certain embodiments, the target backing comprises a highhydrogen diffusion metal (e.g., palladium), has open spaces dispersedthroughout for reduced proton or deuteron diffusion distances, and has ashape and thickness such that all, or virtually all, of the protons ordeuterons that pass through the HEIB target are stopped. Also providedherein are systems, devices, and methods for changing targets in an ionbeam accelerator system. Individually or collectively the ion beamtarget assemblies (and components thereof) may be applied to, forexample, any non-reactor source of high energy neutrons. Embodiments ofthe technology may be employed with high energy ion beam generatorsystems such as those described in, U.S. Pat. Publ. No. 2011/0096887,2012/0300890; U.S. patent application Ser. No. 15/873,664; and2016/0163495 and U.S. Pat. Nos. 8,837,662 and 9,024,261, all of whichare herein incorporated by reference in their entireties.

Non-limiting embodiments of the articles, devices, and systems includethe following. A beryllium (or uranium, lithium, a lithium compound,tungsten, or tantalum) target is bonded to a thin corrugated palladiumtarget backing (e.g., sheet) that is bonded to a water cooled substrate(e.g., copper or aluminum). The thickness of the beryllium is less thanthe penetration depth of the incident protons. The thickness of thetarget backing is sufficient so that all of the protons or deuterons arestopped by the target backing. The target backing is grooved in anypattern that, for example, makes most of the palladium metal arelatively short distance from a surface. The diffusion and solubilityof hydrogen in palladium is extraordinarily high. Excess hydrogen(protons) implanted in the palladium are able to diffuse to a nearbygroove and leave the system before damage occurs to palladium. Thelifetime is very long, limited only by the small damage incident ontothe Be. Palladium thickness and relative amount of grooving is used totune the temperature of the palladium under irradiation to increasediffusion rates. Failure of target would not result in vacuum breach.Any material that has relatively high hydrogen diffusivity may be usedinstead of the palladium. Suitable performance may be obtained withsignificantly cheaper materials such as titanium, vanadium, niobium,zirconium, etc. Besides grooving, any mechanism to reduce diffusiondistances for the hydrogen could also be employed. For example, a porousopen celled palladium (or other material) created from powdermetallurgy, or other, technique could also be used.

We claim:
 1. A system comprising: a) a high energy ion beam target (HEIBtarget) comprising a metal and having a top surface and a bottomsurface, wherein said metal is selected from the group consisting of:beryllium, uranium, lithium, tungsten, and tantalum, wherein said highenergy ion beam comprises protons and/or deuterons, wherein said HEIBtarget generates neutrons when exposed to a high energy ion beam, andwherein said HEIB target has a thickness between said top and bottomsurfaces that is less than the penetration depth of protons or deuteronsin said high energy ion beam; and b) a target backing comprising a highhydrogen diffusion metal (HHDM), wherein said target backing has openspaces dispersed throughout such that the proton or deuteron diffusiondistance is reduced throughout said target backing compared to if saidtarget backing was a solid piece without said open spaces, wherein saidtarget backing is configured to be positioned in contact with saidbottom surface of said HEM target, and wherein said target backing has ashape and thickness such that all, or virtually all, of said protonsand/or deuterons in said higher energy ion beam that pass through saidHEM target are stopped by said target backing when it is positioned incontact with said HEIB target.
 2. The system of claim 1, wherein saidopen spaces are selected from: pores, grooves, holes, corrugations,channels, open cells, honeycomb cells, irregular openings, or anycombination thereof.
 3. The system of claim 1, wherein said targetbacking is attached to, or configured to be attached to, said bottomsurface of said HEIB target by brazing, welding, soldering, diffusion,or bonding.
 4. The system of claim 1, further comprising: c) a cooledsubstrate.
 5. The system of claim 4, wherein said target backing isattached to, or configured to be attached to, said cooled substrate. 6.The system of claim 1, wherein said HEIB target comprises: i) a firstlayer comprising said metal, and ii) a second layer comprising a metaldifferent than used in said first layer selected from the groupconsisting of: beryllium, uranium, lithium, tungsten, and tantalum. 7.The system of claim 4, wherein said cooled substrate comprises copperand/or aluminum.
 8. The system of claim 1, wherein said HEM target has athickness between 2 mm and 25 mm, and a diameter between 25 mm and 150mm.
 9. The system of claim 1, wherein said thickness of said targetbacking is between 2 mm and 10 mm.
 10. An article of manufacturecomprising: a) an ion beam target assembly, wherein said ion target beamassembly comprises: i) a high energy ion beam target (HEIB target)comprising metal and having a top surface and a bottom surface, whereinsaid metal is selected from the group consisting of: beryllium, uranium,lithium, tungsten, and tantalum, wherein said high energy ion beamcomprises protons and/or deuterons, wherein said HEIB target generatesneutrons when exposed to a high energy ion beam, and wherein said HEIBtarget has a thickness between said top and bottom surfaces that is lessthan the penetration depth of protons or deuterons in said high energyion beam; and ii) a target backing comprising a high hydrogen diffusionmetal (HHDM), wherein said target backing has open spaces dispersedthroughout such that the proton or deuteron diffusion distance isreduced throughout said target backing compared to if said targetbacking was a solid piece without said open spaces, wherein said targetbacking is attached to said bottom surface of said HEM target, andwherein said target backing has a shape and thickness such that all, orvirtually all, of said protons or deuterons in said higher energy ionbeam that pass through said HEIB target are stopped by said targetbacking.
 11. The system of claim 10, wherein said open spaces areselected from: pores, grooves, holes, corrugations, channels, opencells, honeycomb cells, irregular openings, or any combination thereof.12. The system of claim 10, wherein said target backing is attached tosaid bottom surface of said HEM target by brazing, soldering, welding,or diffusion bonding.
 13. The system of claim 10, further comprising: b)a cooled substrate.
 14. The system of claim 13, wherein said cooledsubstrate comprises copper and/or aluminum.
 15. The system of claim 10,wherein said HEM target comprises: i) a first layer comprising saidmetal, and ii) a second layer comprising a metal different than used insaid first layer selected from the group consisting of: beryllium,uranium, lithium, tungsten, and tantalum.
 16. The system of claim 10,wherein said HEM target has a thickness between 2 mm and 25 mm, and adiameter between 25 mm and 150 mm.
 17. The system of claim 10, whereinsaid thickness of said target backing is between 2 mm and 10 mm.
 18. Thesystem of claim 10, wherein target backing comprises a core of solidvanadium that is coated with a thin film of palladium.
 19. The system ofclaim 10, wherein at least 95% of said HEM target is said metal.
 20. Asystem comprising: a) an ion source configured to produce an ion beam;b) an accelerator operatively coupled to said ion source and configuredto receive said ion beam and accelerate said ion beam to generate anaccelerated ion beam; c) a target chamber configured to receive saidaccelerated ion beam; and d) a target changing mechanism, wherein saidtarget changing mechanism is configured to: i) hold a plurality oftargets, wherein each target, when struck with said accelerated ion beamin said target chamber generates neutrons, ii) hold one of saidplurality of targets in a first position that is inside said targetchamber and is in the path of said accelerated ion beam, while holdingthe remaining targets outside said target chamber, and iii) move thetarget in said first position to a position outside said target chamber,and move one of said remaining targets into said first position insidesaid target chamber.